The length of the feed line/coax should be long enough to get from the radio to the antenna with some extra in case things need to be moved around some. There is no 'perfect' length. Too much is definitely better than not enough. After that, it's more or less whatever it takes.
The myth about feed line lengths is because there are certain lengths that can be used in -particular- circumstances that can be beneficial. Those circumstances are not all that common, and certainly don't apply to a typical dipole, or vertical antenna. If you can get the antenna at least close to a 50 ohm input impedance the length of the feed line makes no difference at all. Basically, tune the antenna, not the feed line!
- 'Doc
The myth about feed line lengths is because there are certain lengths that can be used in -particular- circumstances that can be beneficial. Those circumstances are not all that common, and certainly don't apply to a typical dipole, or vertical antenna. If you can get the antenna at least close to a 50 ohm input impedance the length of the feed line makes no difference at all. Basically, tune the antenna, not the feed line!
- 'Doc